A connector arranges the proper mutual positioning and clamping force between flare and port. The intended for sealing flare's surface (which is an integrated part of flare's abutment surface) mates with its counterpart onto the port's seat and creates the seal. Currently, there are two families of standardized mass-produced brake connectors utilized in automotive industry.
The first class is based on the interaction of a male type (convex) seat situated inside connector's port (hole/recess) and extending into it. Accordingly, a female (concave) flare with its inner surface dedicated for abutment against the seat with the purpose of forming the fluid seal, is required. This class is represented by the JASO/SAE connector design. Its nominal sealing surfaces' shape is a frustum (portion of a cone with cut off vertex). Its double inverted flare (funnel or trumpet) has inner (concave) frustum which is intended for sealing onto “external” (convex) frustum (seat) of the port. The design is defined by SAE J533 and JASO F402 standards (which are similar to each other).
The second class of tube flared connectors incorporates the reversed combination—a female type (concave) seat interacting with a male type (convex) flare. This class is represented by the ISO connector design. It incorporates the flare (bubble) with its external surface dedicated for abutment against the seat with the purpose of forming the fluid seal. Nominal shape of its sealing surface is also frustoconical. The frustoconical concave seat is an integrated part of the connector port (hole/recess)—there is no any portion extending into the port. The ISO design is defined by the SAE standard J1290.
Good and robust connector sealing may be expected only if adequate clamping force is developed onto the contact ring of sufficient size between the sealing surfaces. There is a fundamental shortcoming of frustum to frustum mating. A ring of contact may be expected only if the axes of both the flare and the port coincide. Otherwise, it is common that the result of cone frustum side surfaces crossing (i.e., having a geometry entity which belongs to both frustums) is just a single point. Typically a connector has to provide some degree of robustness, since a ring-like shaped initial contact may not be always anticipated. Certain amount of self-adjustment or reasonable sustained deformation during connector's securing is expected when initial contact takes place at a single point. That usually corrects the mutual positions of the components toward development of a ring-like contact area between the flare's and the seat's sealing surfaces. However, there are certain known limitations of the degree of robustness of current state of the art frustum-to-frustum connectors.
Under certain conditions friction may lock the flare in a misaligned state against port's seat. Simply put, if the initial contact occurs on a single point, then the flare gets locally squeezed there between the nut and the port. If the effective friction coefficient at that squeezed area becomes greater than certain threshold then the flare gets locked. Such locking inhibits self-adjustment as mutual motion of the components becomes restricted, and extra torque is not able any more correct poor initial contact into an uninterrupted ring-like line. At the same time reasonable torque increase may also become not sufficient to provide the deformation, which becomes required to close the gap between the sealing surfaces. In this case further torque increase leads to squashing of joint's components, which in turn may permanently preclude development of the seal.
There are two groups of causes, which are potentially able to lead to a single point initial contact. First group is related to misalignment of the frustums (and this is applicable even if the frustums have ideal shapes without deviations/defects). This group of causes is usually associated with an external disturbance. Usually some degree of initial misalignment is unavoidable and requires some extra torque to overlap the misalignment by connector's self-adjustment. An external disturbance may increase initial misalignment or cause difficulty to correct it. For example a side force, applied onto the tube in the direction which helps to increase that initial misalignment, unfavorably changes the balance of the forces into the connector. Accordingly more extra torque becomes necessary for additional self-adjustment (sufficient to overlap new balance of the forces caused by that disturbance). Generally an external disturbance consumes certain portion of connector's available self-adjustment capacity and therefore increases chances of initial single point contact and further locking. The second group of causes is related to common manufacturing process variations and defects. A single point initial contact between the frustums (alternatively, sort of a chain of single points) may also occur because of deviations from their intended shapes or defects even if the frustums are perfectly aligned. On top of that some local defects (sharp edges, scratches, bulges, chips etc) at the single point of contact greatly increase effective local friction. Accordingly those defects may greatly inhibit connector robustness leading to significant increase of the probability of locking.
The following details regarding flare endforming process are useful for understanding innate disadvantages of the existing art comparing with the present invention.
By the design intent ISO flare's cone angle is always less than port's one. Therefore when ISO flare mates with its port, initial contact is supposed to occur at the small flare frustum diameter (flare's end around tube's passageway hole). However the very same flare's area is most vulnerable to deviations. This area is basically the former surface of the tube's tip prior to the endforming (a process to form up a flare onto “raw” tubing). Tube's tip is very dependent on quality of the cutting off operation, which is necessary to obtain required tube length. Plain conditioning of tube's tip surface after the cutting off operation (brushing, chaffering etc) can not assure ideal circumference there and its perpendicularity to tube's axe. The coining (another conditioning process, which is well known as effective way to obtain precise surface) cannot be applied at this area, as no buttress is available inside flare's “bubble” during the endforming process. Ambiguity of tube tip surface is also combined with variation of the endforming process. Essentially, current manufacturing practice provides limited capability to form flare's area around passageway hole of the tube. The SAE standard J1290 also admits such unpredictability. Its drawing, which defines ISO flare geometry, notes the area around passageway hole “as formed”. That is serious disadvantage of the ISO flare. This is the most important portion of its sealing surface, which is intended to be the datum while mating, and which coincides with one of the less predictable area of the flare. Unavoidable deviations and defects there directly responsible for interrupted line of the initial contact and corresponding difficulties to develop the seal.
The other type (SAE/JASO double inverted flare) also has unpredictable “as formed” area around its small frustum diameter. The endforming process shapes double inverted flare in such a way that the metal into the die flows “with the funnel” i.e. toward small frustum diameter. Only in case of maximum material condition it is possible to expect the minimum size of small frustum diameter (i.e. on its lower specification limit). Otherwise its actual size very depends on actual amount of the metal, which is available within the die. The size also depends on how much the tooling is worn out. Thus it is more probable to get bigger actual size of that diameter. Both specifications (SAE and JASO) also admit unpredictability there and stipulate relatively loose tolerance for this diameter. For the most popular tube sizes of 5/16″ and ¼″ the allowance is 0.75 mm by the SAE standard and 0.70 mm by the JASO, which is comparable to the nominal size of 1.1 mm of sealing surface seat length. That is why actual small diameter of flare's frustum can either be greater or smaller than the small diameter of seat's frustum. Accordingly it is possible to have two different ways of mating.
If the actual size of the seat's frustum small diameter is greater than the flare's one then initial contact occurs by the seat's top somewhere onto the sealing surface of the flare. That is a preferred way of mating because this is the smooth coined sealing inner surface of the flare which makes initial contacts with the seat. Accordingly the probability of locked misalignment is very low and full-scale connector's self-adjustment capacity can be expected.
The other (unwanted) way happens if seat's diameter is less than flare small frustum diameter. In this case initial contact occurs by the flare's small frustum diameter somewhere onto the seat. Unfortunately this is quite probable due to mentioned above limited capability of the manufacturing process. On top of unpredictability of the size of flare's small diameter it is also quite probable to get a defect or deviation there. And as it was explained before a local defect (sharp edge, scratch, bulge, chip etc) may greatly increase effective local friction. Moreover, lack of available metal during endforming may become “asymmetrical” which in turn can lead to uncompleted circumference around actual small diameter area. As the result flare frustum may get either voided or skewed around its small diameter. Such incomplete circumference may nevertheless become fit to service as actual datum during mating onto seat's sealing surface. Needless to say, that each void provides a potential leak path, which may or may not be eliminated by additional torque (deformation). Propensity of a defect combined with initial single point contact corresponds to high probability of locked misalignment. Thus, connector's self-adjustment capability may deteriorate significantly resulting difficulties to develop the seal.
On top of the fact that small frustum diameter is an unpredictable “as formed” area, it is very difficult to detect deviations of double inverted flare there. If the small diameter is not completely formed it is hard to define where exactly it should be measured. It is much more complicated than usual to use “inside the tube” generic measurement tools like a caliper on repeatable and reproducible way. Because of cost related reasons and lack of criteria for thoroughness of that diameter, all available technologies like machine vision systems, laser scanning, X-ray etc are not utilized as an in-process 100% check. Current industry wide practice rather relies on manual sorting on as needed basis. Unfortunately current manufacturing and quality control practices allow relatively easy escape for defects and deviations at this “as formed” area of JASO/SAE flare.
The problem of relatively easy escape of a quality defect is also applicable to the JASO/SAE seat. It is also difficult to control the shape and the dimensions of such seat and its surrounding area because of their “inside the hole” location. On top of that, a convex (male) seat situated inside of its port has many other disadvantages against a concave (female) integrated into its port one.
The shape of a male seat extending into the port is obviously more complex than a female one, and it, thus, requires more steps to manufacture a male seat. The parts are typically formed using a metal cutting process. The female port according to the present invention requires a step to form the hole for the port, a step to cut the thread into the hole and a last step to finish the bottom portion of the hole to make it suitable for usage as a seat. A male seat, as taught by JASO/SAE, requires all of the above steps plus forming and finishing steps for the part of the seat extending into the port. Even when rolling and cold forming technologies may help to combine some of the operations, the additional body extending into the port invariably requires extra steps.
Correspondingly, the tooling to manufacture a female seat port according to the present invention is simpler, and, thus, less expensive.
Regarding the quality control of finished products, the female seat port according to the present invention is more easily controlled than a male seat extending into the port. Controlling an internal seat requires special equipment to measure and control both dimension and surface roughness internally in the port. Since the female seat is easily accessible from the outside, the quality control is simpler.
Despite of its disadvantages the SAE/JASO ports are still widely utilized because there is a misperception that SAE/JASO flare provides more robustness to the assembly process than the ISO one. Seemingly easy repair in fact hides acquired defect (flow reduction) and may lead to untimely part replacement on the field. Since extra torque engages connector's self-adjustment, it is a common practice to apply increased torque in order to repair connector, if there is a leak. Usage of excessive extra torque is virtually undetectable in case of a convex (male) seat. (In case of the ISO flare excessive torque most likely leads to a crash of the flare and a replacement). A female flare usually envelops seat and eventually translates all the deformations (sustained due to excessive torque) onto the seat. Accordingly initial geometry of such male (convex) seat may get changed significantly which may lead to a substantial reduction of the diameter of the passage, which in turn may cause a considerable decline in flow rate.
The use of a female (concave) seat is superior to the use of a male (convex) seat, and, thus, the use of an external abutment surface of the flare is superior to the use of a flare with internal abutment surface, in terms of sealing capability, flow performance, manufacturing feasibility and quality control. Accordingly usage of the combination of a concave (female) seat with an external (convex/male) flare provides better method to form a fluid-tight seal comparing to the combination of a convex (male) seat with a concave (female) flare.
Correspondingly an improved brake tube flare connector based on the combination of a concave (female) seat with an external (convex/male) flare is needed. Thus, in order to improve sealing robustness by reducing sensitivity to the variations and disturbances, existing male type flare of the ISO design must targeted as the basis and subject for further improvement.
There are two know solutions associated with incorporation of a non-frustoconical shape for the sealing surface. They provide only partial improvement to the existing art as only the misalignment related problem (the first mentioned above group of causes) can be resolved. In theory, a crossing between either two spheres or sphere with cone is always a circumference. Therefore a circumference as initial contact line between the flare and the seat can be expected even if their axes are misaligned within reasonable span. The first one is U.S. Pat. No. 1,894,700, granted Jan. 17, 1933 to Parker, A. L A R. teaching incorporation of zones of sphere for both the flare and the seat. The second one is the US patent application No. 20070194567 published on Aug. 23, 2007. It stipulates incorporation of zone of sphere for the seat only which to be utilized with a standard JASO/SAE flare. Both designs are not resilient to the second group of the causes as unavoidable deviations from ideal shape and local surface defects still make a single point initial contact possible. Besides, both of them belong to the first family of the connectors (based on male/convex seat interacting with female/concave flare). The present invention belongs to the second family (female/concave seat interacting with male/convex flare) enabling the method to form fluid-tight seal, which is superior over the first one.